1. Field of the Invention
The present invention relates to a tunneling magnetoresistive element mounted on a magnetic reproducing apparatus, for example, a hard disk device, or the like, or another magnetic sensing device. Particularly, the present invention relates to a tunneling magnetoresistive element which can stably produce a rate of change in resistance, and which can be formed with high reproducibility, and a method of manufacturing the same.
2. Description of the Related Art
FIG. 21 is a partial sectional view illustrating the structure of a conventional tunneling magnetoresistive element.
In FIG. 21, reference numeral 1 denotes an electrode layer made of, for example, Cu, W, Cr or the like.
An antiferromagnetic layer 2, a pinned magnetic layer 3, an insulating barrier layer 4 and a free magnetic layer 5 are laminated in turn to form a multilayer film 6 on the electrode layer 1.
The antiferromagnetic layer 2 is made of an existing antiferromagnetic material such as a NiMn alloy film or the like, and heat treatment of the antiferromagnetic layer 2 produces an exchange coupling magnetic field between the pinned magnetic layer 3 made of a ferromagnetic material such as a NiFe alloy film or the like and the antiferromagnetic layer 2 to pin the magnetization direction of the pinned magnetic layer 3 in the Y direction (height direction) shown in FIG. 21.
The insulating barrier layer 4 is made of an existing insulating material such as Al2O3 or the like, and the free magnetic layer is made of the same material as the pinned magnetic layer 3, such as a NiFe alloy film or the like.
Referring to FIG. 21, bias layers 9 made of a hard magnetic material such as a Co—Pt alloy film or the like are formed on both sides of the multilayer film 6 in the track width direction (the X direction shown in the drawing).
The bias layers 9 supply a bias magnetic field to the free magnetic layer 5 in the X direction shown in the drawing to orient the magnetization direction of the free magnetic layer 5 in the X direction.
As shown in FIG. 21, an electrode layer 10 is formed on the multilayer film 6 and the bias layers 9.
The tunneling magnetoresistive element serves as a reproducing magnetic element utilizing a tunneling effect for detecting a leakage magnetic field from a recording medium. When a sensing current is supplied to the multilayer film 6 from the electrode layers 1 and 10 in the Z direction shown in the drawing, a tunneling current changes based on the magnetization relation between the free magnetic layer 5 and the pinned magnetic layer 3 to cause a change in resistance, thereby detecting a recording signal by the change in resistance.
However, the structure of the tunneling magnetoresistive element shown in FIG. 21 has the following problem.
Since the sensing current supplied from the electrode layers 1 and 10 flows not only through the multilayer film 6 but also through the bias layers 9 formed on both sides of the multilayer film 6 to fail to obtain a TMR effect, thereby significantly deteriorating the function and properties of the reproducing magnetic element.
FIG. 22 shows another tunneling magnetoresistive element having a structure which is improved for resolving the above problem.
Referring to FIG. 22, insulating layers 7 made of, for example, Al2O3 or the like, are formed on both sides of the multilayer film 6 in the track width direction (the X direction shown in the drawing).
By forming the insulating layers 7, a plane surface extends on the same plane as the upper surface of the multilayer film 6, the bias layers 9 made of a hard magnetic material such as a Co—Pt film being respectively formed on the insulating layers 7 with underlying layers 8 of Cr provided therebetween.
Each of the hard magnetic bias layers 9 is formed to further extend from the insulating layer 7 to the upper surface of the multilayer film 6 by a width dimension T1. As a result, the magnetization direction of the free magnetic layer is oriented in the X direction by a bias magnetic field from the bias layers 9.
In the structure shown in FIG. 22, the insulating layers 7 are formed on both sides of the multilayer film 6, and thus the sensing current from the electrode layers 1 and 10 appropriately flows through the multilayer film 6 with less shunt current. Also, in this structure, the bias magnetic field from the bias layers 9 flows into the free magnetic layer 5 from the top thereof, not from the sides of the free magnetic layer 5.
However, the tunneling magnetoresistive element shown in FIG. 22 has the following problem.
As shown in FIG. 22, a bias magnetic field A from the bias layers 9 is oriented in the track width direction (the X direction shown in the drawing) to supply a magnetic field to the free magnetic layer 5 in the X direction. However, at the same time, a magnetic field B oriented in the direction opposite to the bias magnetic field A occurs in the portion of the free magnetic layer 5 which contacts of the extension of each of the bias layers 9 on the multilayer film 6. The occurrence of the magnetic field B destabilizes the magnetic domain structure of the free magnetic layer 5 to cause the occurrence of Barkhousen noise or destabilize a reproduced waveform, thereby deteriorating reproducing characteristics.
As described below, the structure of the magnetic element shown in FIG. 22 causes difficulties in forming the bias layers 9 with high alignment accuracy, causing variations in the width dimension T1 of the extension of each of the bias layers 9. Particularly, the bias layers 9 are formed to extend on a sensitive zone of the multilayer film 6, which substantially exhibits a magnetoresistive effect, and thus the magnetic domain structure of the sensitive zone is significantly destabilized due to the occurrence of the magnetic field B. Also, the extensions of the bias layers 9 to the sensitive region significantly decrease a zone which can exhibit the magnetoresistive effect, thereby deteriorating characteristics.
The occurrence of the magnetic field B is due to the formation of the underlying layers 8 made of Cr between the free magnetic layer 5 and the bias layers 9. The presence of the underlying layers 8 interrupts magnetic coupling between the free magnetic layer 5 and the bias layers 9.
There is thus the idea that the underlying layers 8 are removed to directly joint the free magnetic layer 5 and the bias layers 9. However, without the underlying layers 8, the coercive force of the bias layers 9 cannot be ensured to cause difficulties in controlling crystal orientation, thereby significantly deteriorating hard magnetic properties.
The method of manufacturing the tunneling magnetoresistive element shown in FIG. 22 also has the following problems.
As shown in FIG. 23, after the electrode layer 1, the multilayer film 6 and the insulating layers 7 are formed, the bias layer 9 is formed on the multilayer film 6 and the insulating layers 7.
In FIG. 24, a resist layer 11 is formed on the bias layer 9, and then exposed and developed to form an aperture pattern 11a having a predetermined with dimension in the central portion of the resist layer 11. Then, the bias layer 9 exposed from the aperture pattern 11a is removed by etching to form the bias layers 9 having the shape shown in FIG. 9.
However, it is difficult to form the aperture pattern 11a with high precision at a predetermined portion of the resist layer 11 at the top of the multilayer film 6, which has a very small width dimension, thereby causing variations in the shape of the bias layers 9 to deteriorate reproducibility.
Furthermore, in the step of etching the bias layers 9 exposed from the aperture pattern 11a, a portion of the free magnetic layer 5 below the bias layer 9 is also possibly removed to make it difficult to control the etching time or the like. Since the free magnetic layer 5 is formed to a small thickness of several tens nm, a variation occurs in the properties even when only a small amount of the free magnetic layer 5 is removed.
Also, the structure of the tunneling magnetoresistive element shown in FIG. 22 easily produces a variation in a reproducing gap. As shown in FIG. 22, the length from the lower electrode layer 1 to the upper electrode layer 10 is h1 in the central portion where the bias layers 9 are not formed on the multilayer film 6, while the length is h2 in the portion where the bias layers 9 are formed on the multilayer film 6, the length h2 being longer than the length h1. Therefore, a variation occurs in the thickness of the reproducing gap within the width dimension of the multilayer film 6 in the track width direction (the X direction shown in the drawing), easily causing an adverse effect on the reproducing characteristics.